Narrow Bore Column and Injection Volume

[Bripirate]

I seem to remember that there was a rule of thumb regarding the maximum injection volume that you could/should use for narrow bore columns. I currently have a method that uses a 2.1 x 250 mm column with a 10 µL injection volume. The chromatography looks fine but I wonder how much I can increase the injection volume before I see issues. This is an ion chromatography method with suppressed conductivity detection.

[tom jupille]

No single simple answer to that one. Ultimately, what you should do is to run a series of increasing-volume injections and see how far you can push it.

that said, if your sample diluent is weaker than your mobile phase, then you can do some *big* injections (I've done 10 mL injections in non-suppressed IC where the sample was essentially deionized water). On the other hand, if your diluent is stronger than your mobile phase (e.g., a brine solution), then even a couple of microliters may be too much.

If the diluent *is* the mobile phase (or at least has equivalent ionic strength) then a good rule of thumb is to keep the total extra-column volume below about 1/3 of the volume of the narrowest peak of interest. That should give you 95% of the column's resolution. Remember that injection volume is only part of this!